Description
The CONTACTGENERATE Case Control command automatically generates contact surfaces for all “parts” of the model and an automatic pairing of all surfaces as potential contact pairs. This contact surface generation is referred to as Automated Surface Contact Generation (ASCG). (We define the term “parts” in the following discussion.)
The numbering for generated contact surfaces is determined by property identification values (PID’s that appear on property entries). Suppose, for example, we have a set of elements that reference a property entry with a PID of 25. The ASCG will examine all of the elements that reference this property entry and determine which element faces associated with this set of elements are exterior faces – faces that can come into contact with other exterior faces on different element sets. The set of exterior faces from the elements that reference the property entry with a PID of 25 constitutes a contact surface with an identifier of 25. The identifier of 25 is used as the CSID (contact surface identifier) of the generated contact surface. The generated contact surface is a list of faces (segments in BSSEG terminology) that are exterior faces for all of the elements that reference a property entry with a PID of 25. The generated contact surface is treated like a user defined BSSEG entry and is equivalent to an actual BSSEG entry. The generated contact surface does not appear as an actual BSSEG entry in the Bulk Data.
A common occurrence is to have two or more blocks of solid elements come into contact. The ASCG will automatically “skin” any block of solid elements to obtain the contact surface for the block of elements. If a block of solid elements references a property entry with a PID of 37, the skinning of the block will produce a generated contact surface with a CSID (contact surface identifier) of 37.
A set of blocks that references the same property entry will be referred to as a “part”. Suppose a set of hexahedral elements defined by CHEXA entries all reference a PSOLID entry with a PID of 115. We will have a set of elements that all have the same topology and all reference a single property entry. (A part will not be a mixture of elements such as solid elements plus shell elements.) The generated contact surface associated with this part will have a CSID of 115.
The ASCG automatically generates contact surfaces for all parts of the model. Every part of the model that has a set of exterior faces and is associated with a property entry, and hence a unique PID, will generate a contact surface associated with the PID. The generated contact has a CSID that can be traced back to the PID on some property entry. You may refer to all the generated contact surfaces in the same manner as any contact surface defined with a BSSEG entry just by referencing the CSID of the generated surface.
The matrix of all parts of the body that can contact each other is full. That is, if there are N unique parts in the model, then there is an N x N matrix that identifies all the contact pairs. This includes the diagonal of the matrix, which means that parts can contact themselves. The CONTACTDELETE command can be used to remove contact pairs from the matrix that you know in advance will not contact one another.
Format
CONTACTGENERATE, ptype, self, sfact, mu, maxad, capturetol
Example
CONTACTGENERATE, 2, OFF, 0.1
| Option | Definition | Type | Default |
|---|---|---|---|
| ptype | Penetration type:
2 = Symmetric general contact 4 = Symmetric welded contact |
Integer | 2 |
| self | Self contact flag: This flag indicates whether or not to allow surfaces to contact themselves (self contact). | Character, either ON or OFF | ON |
| sfact | Stiffness scaling factor: This factor is used to scale the penalty values. Penalty values are forces that are calculated internally to enforce contact. See Remarks 2 and 5. | 0.0 < Real ≤ 1.0 | 0.2 |
| mu | Coefficient of static friction. | Real ≥ 0.0 | 0.0 |
| maxad | Maximum activation parameter: See Remarks 3 and 4. | Real ≥ 0.0 | 0.5 |
| capturetol | Capture tolerance parameter for tied contact pairs: This value is used for tied contact. Regions of opposing contact surfaces within a certain tolerance are tied together. See Remarks 4 and 5. | Real ≥ 0.0 | 0.05 |
Remarks
- The contact identification numbers are generated for each surface using PID’s on the property entries. See the above description of CONTACTGENERATE.
- The contact enforcement algorithm uses a penalty method approach. The penalty method automatically calculates a set of forces to eliminate overlap of any contact surfaces. The factor sfact can be used to scale the forces that are generated from the penalty method.
- Values of sfact greater than 0.5 are not recommended; a value of sfact greater than 0.5 can lead to numerical instability.
- The parameter maxad can be used to prevent unnecessary generation of contact. Contact is only generated if the distance from any contact surface primary node to the potential secondary node is less than MAXAD * Lc, where Lc is a characteristic segment length determined from the faces on the contact surface.
- The stiffness parameter, friction coefficient, penetration type, maximum activation distance, and capture tolerance specified on this line will be applied to all surface pairs generated by this command. Individual surface pair parameters can be redefined using the BSCONP entry.
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The parameter capturetol is used for tied contact. Regions of opposing contact surfaces that are within a distance CONTACTOL * Lc, where Lc is a characteristic segment length determined from the faces on the contact surfaces, are tied together.